1. Field of the Invention
The present invention relates to a polymeric monofilament and to a felt fabricated therefrom.
2. Description of the Prior Art
Polymeric monofilaments, in general, are produced by melt-extrusion processes as is well known in the art. A polymeric resin is melt-extruded into continuous strand monofilaments by an extruder equipped with a monofilament die, and then the resulting monofilaments are quenched to form solid monofilaments. Thereafter, the solid monofilaments are subjected to a stretch drawing process, also known as an orientation process, which includes one or more steps of alternating heat stretching and quenching procedures, to impart physical strength.
Woven endless belts for conveying and guiding products under manufacture are widely utilized in various industrial processes and are one group of numerous applications where polymeric monofilaments are used extensively. Many of such conveyer belt applications involve harsh chemical and temperature environments in which ordinary polymeric materials cannot withstand.
As an illustration of conveyer belt applications in which conveyer belts are exposed to harsh environments, the felts for papermaking machines are described below. A papermaking machine, in essence, is a device for sequentially removing water from paper furnish. A typical papermaking machine is divided into three sections: forming, wet-press, and dryer sections. In the forming section, the slurry of paper furnish and water is deposited on a forming grid and water is drained, leaving a paper web of about 75 weight percent water content. The resulting web is carried into the wet-press section on a felt (wet-press felt) and passed through one or more of nip presses to reduce the water content of the web to below about 65 weight percent. The web is then carried to the dryer section and dried by contacting hot dryer cylinders on a felt (dryer felt) to reduce the water content of the web to below about 8 weight percent.
Although the felts for different sections of papermaking machine must be designed and fabricated to meet specific needs essential to each section, the felts must possess the general characteristics of dimensional stability, resistance to chemical and thermal degradations, resistance to abrasion, resiliency and tenacity. Both metal and synthetic polymers have been used to fabricate the felts with varying degree of success. Metal fabric felts provide superior thermal characteristics, but are difficult to handle, have poor flexural resistance and are prone to chemical attack and corrosion. These disadvantageous characteristics of metal fabric felts led to a wide acceptance of fabric felts made from a variety of synthetic polymers such as polyolefins, polyamides and polyesters. However, such synthetic polymer felts also exhibit certain disadvantages. Polyolefin felts, for example, are dimensionally stable but have low thermal stability and are not resistant to the chemicals utilized in the papermaking process. Felts made from polyesters provide dimensional stability, and are resistant to abrasion and chemicals, but are prone to high temperature hydrolysis. Felts made from polyamides, such as nylon 6 and nylon 6,6, provide abrasion resistance, resiliency and tenacity, but do not have the required dimensional stability.
There are many commercially available specialized synthetic polymers that are useful for the felt application. Currently, one of the most widely used synthetic polymers to fabricate felts for papermaking machines are polyamides having a long carbon-chain, such as nylon 10, nylon 12, nylon 6/10, and nylon 6/12. Such polyamides provide tenacity, resiliency and abrasion resistance as well as dimensional stability. Polyaryletherketone fabrics also have been utilized in the felt applications as disclosed in U.S. Pat. No. 4,359,501 to DiTullio. U.S. Pat. No. 4,159,618 to Sokaris discloses yarns fabricated from liquid-crystal polymers, such as aramides, that are useful in the manufacture of woven felts. Although these specialty polymer felts provide good properties that are required in the papermaking felt applications, the high cost of these specialty polymers precludes wide acceptance of such felts. Consequently, it would be desirable to have less expensive polymeric materials that exhibit the required characteristics suitable for the felt application.
The present inventors investigated polyphenylene ether/polyamide blend compositions to create blend compositions that are highly suited for use in various monofilament and conveyer belt applications. Although, as is known in the art, polyphenylene ethers and polyamides are incompatible polymers and the two polymers must be compatibilized to form blend compositions of any use, there are numerous prior art teachings of polyphenylene ether/polyamide blend molding compositions, e.g., U.S. Pat. Nos. 3,379,792 to Finholts, 4,315,086 to Ueno et al., and 4,732,938 to Grant et al. However, the use of polyphenylene ether/polyamide blends for monofilament applications has not been considered in the prior art. This is because it is known in the art that only the blend compositions of compatible polymers can successfully be fabricated into useful monofilaments without breaking the monofilaments during the stretch drawing process and that the compatibility level attained by the prior art polyphenylene ether/polyamide blend molding compositions are not sufficiently high enough to produce useful monofilaments. The compatibility of the two polymers in the prior art polyphenylene ether/polyamide blend compositions are not so high as to form homogeneous blend, and they contain relatively large domains of one polymer within the continuous matrix of the other polymer. Such partially compatible polyphenylene/polyamide blends cannot be used to produce monofilaments since the extrusion of dimensionally uniform monofilaments from such partially compatible blends is not practical and the resulting monofilaments do not have uniform physical properties throughout the length of the filaments. In addition, the monofilament fabricated from such partially compatible blends cannot successfully be subjected, without breaking the monofilament, to the stretch drawing process, which is a necessary process to impart strength to the monofilament.
It would therefore be desirable to provide highly compatible and homogeneous polyphenylene ether/polyamide blend compositions that are suitable for fabricating quality monofilaments and conveyer belt fabrics made therefrom.